https://dev1.mystudentsprogress.com/testposting/smallform.html --> this is using method = "post" and works fine with a small number of fields, click save and it calls a cf template that simply says "index.cfm here"
https://dev1.mystudentsprogress.com/testposting/formget.html ---> this is using method = "get" and also works fine, click save and it calls a cf template that simply says "index.cfm here"
https://dev1.mystudentsprogress.com/testposting/formpost.html --> this is using method = "post" and it barfs, click save and you get an error 500 page
And once this happens the "next" call for even the succesfull pages returns a blank page i.e. go here:
https://dev1.mystudentsprogress.com/testposting/smallform.html and click save
No go here again and click save:
You might investigate the postParametersLimit and postSizeLimit values in your server's neo-runtime.xml file. I suspect you'll need to increase the values for those two settings. Remember to back up this file before making any changes. You will need to restart the CF server to apply any changes made to the settings in this file.
See the CF 9.0.2 release notes for more information: http://helpx.adobe.com/coldfusion/release-note/coldfusion-9-0-update-2 .html
To clarify. I would increase the postParametersLimit value to handle a larger number of form fields. I would increase the postSizeLimit to handle large form submissions, such as when uploading (posting) files from client to server.